Display system using cathode ray tube deflection yoke non-linearity to obtain curved strokes



Nov. 10, 1970 N. CRISCIMAGNA ET L DISPLAY SYSTEM USING CATI'IODE RAY TUBE DEFLECTION YOKE NON-LINEARITY TO OBTAIN CURVED STROKES Filed Jan. 12, 1968 FIG.I

MAIN XAY POSITIONING SIT PROCESSOR DATA 2 Sheets-Sheet 1 CHARACTER COMPLETE SIGNAL 64% START CHARACTER GENERATION SIGNAL CHARACTER SELECTION SIGNALS STROKE STORAGE REGISTER ENOPOINT SIGNALS IOA REGISTER Y D/A CONVE RTER OUTPUT NEXT STROKE 62A SIGNAL LAST STROKE SIGNAL REGISTER CONVERTER INTENSITY CONTROL CIRCUIT DECODER -DELAY CIRCUITS MAIN POSITION CONTROL CIRCUITRY CHARACTERDEFLECTION YOKES 50 MAINDEFLECTIONYOKES CATHOOE RAY TUBE 5O LAST STROKE INVENTORS TONY N. CRISCIMAGNA DONALD J. HINKEIN ATTORNEY US. Cl. 340-324 12 Claims ABSTRACT OF THE DISCLOSURE A character display system in which a character is generated on the face of a cathode ray tube using a plurality of predetermined straight and curved line strokes generated in a predetermined order. Both straight and curved line strokes are generated without the need of special wave shaping circuitry for producing the deflection yoke currents. A straight line is generated by providing matched operation of the nonlinear current vs. time characteristics of the X and Y deflection yokes, whereby a straight line stroke is obtained despite the non-linearity of the indidivual X and Y characteristics. A curved line stroke is generated by providing mismatched operation of the non-linear X and Y deflection yoke current vs. time characteristics, whereby the existing non-linearity is used to advantage to permit a curved line stroke to be obtained without requiring special wave shaping circuitry.

BACKGROUND OF THE INVENTION The present invention relates to means and methods for displaying data on the face of a cathode ray tube, and more particularly to improvements in display system of the type in which a vector or character is generated on the face of a cathode ray tube using a plurality of successively produced strokes of appropriate shape and direction.

A particularly desirable embodiment of a stroke generation display system is disclosed in US. Pat. No. 3,325,803. In the system of this patent, a character is formed using straight line strokes of variable length and direction. An important feature of the system of the patent is that these straight line strokes are generated without the need of special waveform shaping circuitry for producing the deflection yoke currents, as was previously required in the art. This is accomplished in the prefered embodiment of the patent by critically damping the deflection yokes, by making the time duration of each stroke constant regardless of stroke length,

and by matching the timing and waveform characteristics of the X and Y deflection yokes so that a linear stroke is produced even though the current rise in each deflection yoke is non-linear.

While the system of Pat. No. 3,325,803 permits achieving significant circuit economies because of the elimination of special wave shaping circuitry, it has the obvious disadvntage that, because characters must be formed of straight line strokes, the generation of curved portions of characters requires many strokes and forces a compromise between the number of segments required to approximate the character, and the time available for character generation. Of course, the capability of generating curved strokes can be added to the system of the patent using known wave shaping techniques, such as Lissajous waveforms, mask scanning, special function generators, etc., but the addition of the hardware required by these wave shaping techniques would United States Patent significantly detract from the economies realized by the approach of the patent.

BRIEF SUMMARY OF THE INVENTION The primary object of the present invention is to provide the system of the aforementioned patent with the capability of generating curved strokes without significantly increasing the advantageous economical circuitry provided thereby. The present invention achieves this very desirable object by converting the normally considered disadvantage of the non-linearity of the deflection yoke into an andvantage which makes possible the generation of curved strokes without requiring additional wave shaping circuitry, while still maintaining the same cpability for straight line stroke generation. More speccifically, these features are accomplished in accordance with the invention by causing appropriate mis-matched operation of the non-linear X and Y deflection yoke currents in order to provide a curved stroke, and matched operation in order to provide straight line stroke. In a preferred embodiment of the present invention, matched operation in order to generate a straght line stroke in a desired direction is provided in the manner disclosed in the aforementioned patent; mis-matched operation in order to generate a curved stroke is provided by applying driving steady-state currents of appropriate amplitudes to the X and Y deflection yokes at appropriate times with respect to one another, so that the rise of the currents in the X and Y deflection yokes occur over different predetermined portions of their non-linear curves.

It is to be understood that, although the invention is of particular advantage when applied to a system such as disclosed in the aforementioned patent, the invention is not limited to such use, and, from the description to be provided herein, it will be apparent to those skilled in the art that the invention may also be applied to other types of display systems, and wherever else it is of advantage to make use of the non-linear characteristics of a deflection yoke for obtaining a curved trace on a cathode ray tube.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a block and schematic electrical diagram of a preferred embodiment of a display system in accordance with the invention.

FIG. 2 is a graph illustrating a typical non-linear current vs. time characteristic of a deflection yoke, where time is indicated in terms of deflection yoke time constants (TC).

FIGS. 3 and 4 illustrate the manner in which the exemplary characters P and R may be generated on the face of a cathode ray tube in accordance with the invention.

FIG. 5 is a graph illustrating the time of application and the amplitude of the deflection yoke steady-state currents required to generate the strokes which form the character R in FIG. 4.

FIG. 6 is a graph illustrating the resulting X and Y deflection currents respectively flowing in the X and Y deflection yokes during each stroke in response to the applied steady-state currents illustrated in FIG. 5.

With reference to FIG. 1, it is to be understood that each of the blocks illustrated therein represent Well known circuit means which may readily be provided by those skilled in the art. Each such means should be considered as including any input and output gating circuitry necessary or desirable for performing the operations to be described herein. For convenience of illustration, a plurality of related lines is shown as a cable, while a single line is illustrated in the usual manner. It is to be understood that the cables do not necessarily represent the actual physical arrangement of the lines in the system. As is conventional, arrowheads are provided on the lines and cables to indicate the direction of signal flow. Also, the same designations are used interchangeably to represent either a line (or cable) and the signal (or signals) carried thereby.

Now considering the construction and arrangement of the preferred embodiment of FIG. 1, it will be understood that the data necessary for generating the characters in the font are stored, for example, in binary digital form in a stroke storage register 10. Each character is represented in the stroke storage register by a plurality of strokes arranged to be serially outputed in a predetermined order, as required to form the character. The specific manner in which the stroke data stored in the stroke storage register 10 provides for the generation of curved strokes as well as straight line strokes in accordance with the invention will become evident as the description progresses.

The generation of a character is initiated in the preferred embodiment of FIG. 1 by a START CHARAC- TER GENERATION SIGNAL 12A applied to the stroke storage register 10, for example, by a data processor 12. The data processor 12 also identifies the character to be generated by the application to the stroke storage register 10 of CHARACTER SELECTION SIGNALS 12B. In response to the START SIGNAL 12A and CHARACTER SELECTION SIGNALS 12B, the stroke storage register 10 outputs, in parallel, the data signals required for generating the first stroke of the selected character on the face of the cathode ray tube 50. After the first stroke has been generated, an OUTPUT NEXT STROKE SIGNAL 62A is caused to be applied to the stroke storage register '10, which results in outputing of the data signals for the second stroke of the character, and so on, until the data signals for the last stroke of the character have been outputed. After generation of the last stroke, a CHARACTER COMPLETE SIGNALS 64A is produced instead of the OUTPUT NEXT STROKE SIGNAL 62A, and is applied to the data processor 12 to advise that generation of the selected character on the face of the cathode ray tube 50 has been completed.

The data signals outputed, in parallel, from the stroke storage register 10 for each stroke of a character may typically comprise: 1) X ENDPOINT SIGNALS 10A and Y ENDPOINT SIGNALS 10B specifying a particular endpoint to which the stroke is to be directed, (2) T TIME DURATION SIGNALS 10C specifying a predetermined time duration for which stroke generation will be permitted to occur for the stroke, (3) a BLANK- ING SIGNAL 10D specifying whether or not the stroke is to be blanked (i.e., Whether the stroke will be made visible on the face of the cathode ray tube 50), and (4) a LAST STROKE SIGNAL 10E specifying whether or not the stroke is the last stroke of the character.

As shown in FIG. 1, data signals 10A, 10B, '10C, 10D and 10B which are outputed, in parallel, by the stroke storage register 10 for each stroke of a selected character are applied to respective X, Y and T registers 14, 16 and 18, intensity control circuit 20, and last stroke flip-flop 22 for setting in accordance therewith. The outputs 14A and 16A of X and Y registers '14 and 16 are, in turn, applied to respective X and Y digital-to-analog (D/A) converters 24 and 26 for converting the digital outputs 14A and 16A of the X and Y registers 14 and 16 to corresponding analog signals 24A and 26A for application to respective X and Y character deflection yokes 30 of a cathode ray tube 50 in order to produce stroke generation towards the (X, Y) endpoint designated by the X and Y ENDPOINT SIGNALS 10A and 10B. Whether or not the stroke is to be blanked is controlled by the intensity control circuit 20 in response to blanking signal 10D, the output 20A of the intensity control circuit 20 being applied to the intensity control means of the cathode ray tube 50 in a conventional manner. The starting position for generation of a character and appropriate intensity control therefor are also provided in a conventional manner, for example, using MAIN X and Y POSITIONING AND INTENSITY CONTROL SIGNALS 120 provided by the data processor 12 and applied via suitable main position control circuitry 35 to the main deflection yokes 40 and the intensity control means of the cathode ray tube 50.

The time duration of stroke generation from the existing position towards the endpoint specified by the X and Y ENDPOINT SIGNALSA and 10B is determined in accordance with TIME DURATION SIG NALS 10C by applying the output 18A of the T register 18 to a decoder 32 which, in response thereto, applies an output signal to a selected one of delay circuits 55 providing N different delays D1 to D'N. The delayed output signal from the selected delay circuit "55 passes through OR gate 60 to AND gates '62 and 64. Only one of AND gates 62 and 64 is enabled, as determined by inverse enabling signals 22A and 22B applied to AND gates 62 and 64 from the last stroke flip-flop 22 which will have been set in accordance with the last stroke signal 10E. If the stroke being generated is not the last stroke, then AND gate 62 is enabled to cause the delayed signal from OR gate 60 to pass therethrough to produce the OUTPUT NEXT STROK E SIGNAL 62A, which, as mentioned previously, is applied to the stroke storage register 10 to cause outputing of the data signals for the next stroke, thereby ending the present stroke and starting a new stroke. If, on the other hand, it is the last stroke which is being generated, then AJND gate 64 is enabled to cause the delayed signal from OR gate '60 to pass therethrough to produce the CHARACTER COMPLETE SIGNAL 64A which, as mentioned previously, is applied to the data processor 12 to indicate that the generation of the character has been completed. It will be understood that there is no need to change the setting of the X and Y registers 14 and 16 after the last stroke, since, in the preferred embodiment illustrated in FIG. 1, the endpoint of the last stroke is chosen to always terminate at the same point from which the first stroke began.

With further reference to the X and Y digital-to-analog converters 24 and 26 and the X and Y character deflection yokes 30 in FIG. 1, it is to be understood that these are preferably constructed and arranged in the manner disclosed in the aforementioned Pat. No. 3,325,803. Also, uniform intensity control of the cathode ray tube trace is preferably provided for the embodiment of the present invention in the same manner as disclosed in this patent. Such is indicated in FIG. 1 by respective intensity control signals 24B and 26B from X and Y digital-to-analog converters 24 and 26 being applied to intensity control circuit 20 for controlling the cathode ray tube beam intensity in a manner which will produce a constant intensity trace regardless of beam velocity.

Having described how the strokes of a character are initiated and terminated in the preferred embodiment of FIG. 1, and the manner in which the endpoint, time duration, blanking, and intensity digital data provided by the stroke storage register 10 for each stroke are appropriately converted for use by the cathode ray tube 50, it next will be described in connections with FIGS. 26 how the data for each stroke is typically chosen in accordance with the invention for generating both the straight and curved line strokes required for forming a character. For this purpose, FIGS. 3 and 4 are provided illustrating how the two exemplary characters P and R may be generated from appropriately chosen straight and curved line strokes. Also, it will be assumed that each of the X and Y deflection yokes 30 in FIG. 1 have the exemplary nonlinear current vs. time characteristic shown in FIG. 2 in Which the deflection yoke current reaches its steady-state value after approximately 5' deflection yoke time constants (TC), a typical time constant being, for example, 200 microseconds.

For generation of the character P, it will be seen from FIG. 3 that a total of seven strokes are required as follows: straight line stroke 1, from point Xzt), Y= to point X=0, Y=10; straight line stroke 2, from point X=0, Y=10 to point X=3, Y=10; curved line stroke 3, from point X=3, Y=10 to X=4, Y=7.5; blanked straight line stroke 4 from point X= 4, 86:75 to X=0, Y=5; straight line stroke 5 from X=0, Y=5 to X=4, Y=5; curved line stroke 6 from X=4, 36:5 to X=4, Y=7.5; and blanked straight line stroke from X=4, Y=7.5 to X=0, Y=0.

As will be evident from FIG. 4, the first six strokes used for generation of the character R are the same as for the character P. After the sixth stroke, generation for the character R then proceed as follows: blanked straight line stroke 7' (the prime being used to distinguish from stroke 7 for the character P), from X=4, Y=7.5 to X=3, Y=5; straight line stroke 8 from X=3, Y=5 to X=4 Y=0; and blanked straight line stroke 9 from X=4, Y=0 to X=0, Y=0.

The nature of the data required from the stroke storage register 10 in FIG. 1 in order to generate the above described strokes for the characters P and R will now be made evident using FIGS. 5 and 6 which are specifically directed to the strokes required for forming the character R. Since the first six strokes are the same for both of the characters P and R, FIGS. 5 and 6 also apply to the first six strokes of the character P. Specifically, FIG. 5 is a graph illustrating the amplitude and the time of application of the steady-state currents provided for the X and Y magnetic deflection yokes in order to generate the strokes required for the character R, while FIG. 6 illustrates the resulting deflection yoke currents produced in the X and Y deflection yokes 30 in response to the applied steady-state currents illustrated in FIG. 5. The output signals of the digital-to-analog converters 24 and 26 in FIG. 1 are appropriately chosen to produce the applied steady-state current values illustrated in FIG. 5. An important feature of the invention is that the waveform of the signals provided by the D/A converters 24 and 26 are of the same Shape, regardless of whether a straight or curved line stroke is to be generated, since the present invention uses the non-linearity of the deflection yoke characteristics to obtain curving, rather than employing the conventional approach of applying specially shaped waveforms to the deflection yokes.

The generation of the nine strokes forming the character R shown in FIG. 4 will now be described in detail using the graphs of FIGS. 5 and 6. From this exemplary description, it will become evident how the required combination of straight and curved line strokes may be provided in accordance with the invention for generating any other desired character or graphic data on the face of the cathode ray tube.

Stroke 1 In the manner previously described in connection with FIG. 1, generation of the character R is initiated by a START CHARACTER GENERATION SIGNAL 12A applied to the stroke storage register 10 from the data processor 12 along with appropriate CHARACTER SELECTION SIGNALS 12B Which identify the character R as the one which is to be generated. The stroke 1 data signals 10A to 10E for character R are then out puted in parallel from the stroke storage register 10 and applied to respective registers 14, 16, 18, intensity control circuit 20, and last stroke flip-flop 22, for setting in accordance therewith. As illustrated in FIG. 4, stroke 1 is a vertical straight line stroke from initial starting point X=0, Y=0 to endpoint X=0, Y=10. Accordingly, the X and Y ENDPOINT SIGNALS 10A and 10B are chosen to provide a stroke 1 endpoint of X=0, Y=10 by causing the X digital-to-analog converter 24 to produce a zero steady-state current for the X character deflection yoke and a ten unit steady-state current for the Y character deflection yoke, as illustrated for stroke 1 in FIG. 5, the resultant X and Y deflection yoke currents for stroke 1 being illustrated in FIG. 6. Since stroke 1 is not to be blanked, the BLANKING SIGNAL 10D is chosen so that the intensity control circuit 20 does not provide blanking during stroke 1.

As shown in FIG. 6, five time constants are required during stroke 1 for the Y deflection yoke current to rise to the desired Y endpoint of 10 units. Accordingly, the T TIME DURATION SIGNALS 10C from the stroke storage register 10 are chosen so that the decoder 32, in the manner described previously, applies its output signal to a selected delay circuit having a delay which, when taking into account other circuit delays, will provide an overall stroke 1 time duration of five time constants. Also, since stroke 1 is not the last stroke of the charatcer R, the LAST STROKE SIGNAL 10E will be chosen so that the last stroke flip-flop 22 enables AND gate 62. The delayed signal from OR gate will thus pass through AND gate 62 to produce the OUTPUT NEXT STROKE SIG- NAL 62A, which in turn causes the stroke storage register to output data signals 12A to 12E corresponding to stroke 2 of the character R, thereby terminating stroke 1 and beginning stroke 2.

It will be understood that, because stroke 1 only requires movement in the Y direction, a straight line is produced for stroke 1 despite the deflection yoke non-linearity illustrated in FIG. 2.

Stroke 2 When the stroke 2 data signals 12A to 12E for the character R are outputed from the stroke storage register 10, they change the respective registers 14, 16, 18, intensity control circuit 20 and last stroke flip-flop 22 from their stroke 1 settings to their stroke 2 settings. As shown in FIG. 4, stroke 2 is a horizontal straight line stroke from point X 0, Y=10, to the stroke 2 endpoint X=3, Y=10. The Y ENDPOINT SIGNALS 12B of stroke 2 are chosen, as illustrated in FIG. 5, to cause the digital-to-analog converter 26 to maintain the Y steady-state current at a value of 10 units, while the Y ENDPOINT SIGNALS of stroke 2 are chosen to cause the digital-to-analog converter 24 to provide an X steady-state current value equal to the 4-unit X endpoint value for stroke 3, rather than the 3- unit X endpoint value for stroke 2. As will become evident from the description of stroke 3, the reason for this choice of the X endpoint is for the purpose of providing a mismatched relationship between the non-linear X and Y characteristics during stroke 3 in order to generate the curved line required thereby.

Since the X steady-state value of 4 units chosen for; stroke 3 is greater than the required X=3 endpoint, the time duration of stroke 2 is chosen to terminate when the X deflection yoke current rises to the X-=3 endpoint value of stroke 2, which occurs after a time duration of one time constant. Accordingly, the T TIME DURATION SIGNAL 10C for stroke 2 is chosen to cause decoder 32 in FIG. 1 to select a delay circuit 55 which will provide an overall time duration of 1 time contant for stroke 2.

Stroke 2 of the character R, like stroke 1, is not blanked, nor is it the last stroke. The stroke 2 BLANK ING SIGNAL 10C and the LAST STROKE SIGNAL 10E are thus the same for stroke 1 and likewise cause the intensity control circuit 20 to provide a visible trace of stroke 2 on the cathode ray tube 50, and AND gate 62 to again pass the delayed output from OR gate 60 to produce the OUTPUT NEXT STROKE SIGNAL 62A which terminates stroke 2 and begins stroke 3. Also, similar to the situation occurring for stroke 1, stroke 2 will likewise be a straight line despite the deflection yoke non-linearity illustrated in FIG. 2, since only movement in the Y direction is required.

Stroke 3 As will be evident from FIG. 4, stroke 3 of the character R is a curved line stroke from X:3, Y=10 to X=4, Y=7.5. In accordance with the invention, the required curved line is obtained by providing appropriate mis-matched operation of the non-linear X and Y deflection yoke current vs. time characteristics; in other words, by causing the X and Y deflection currents to operate, during stroke 3, over different potrions of their non-linear deflection current vs. time curves, as illustrated for stroke 3 in FIG. 6. As is will known, the deflection produced by a magnetic deflection yoke is approximately proportional to the current flowing therein, so that the presence of a non-linear current vs. time characteristic for a deflection yoke indicates a like non-linearity of the deflection vs. time characteristic.

It will be remembered from the description of stroke 2 that the X endpoint for stroke 2 is chosen equal to the Xl=4 endpoint for stroke 3, rather than to the X=3 endpoint for stroke 2. This choice of the X endpoint during stroke 2 is used to advantage during stroke 3 by choosing the X ENDPOINT SIGNALS 10A for stroke 3 so as to retain the X steady-state signal at a value of 4 units, while the Y ENDPOINT SIGNALS 10B are chosen to provide the required Y=7.5 endpoint for stroke 3, as illustrated in FIG. 5. It will be apparent from FIG. 6 that such a choice achieves the aim of obtaining mis-matched operation of the X and Y deflection yoke current characteristics during stroke 3, since the X deflection current operates over the last portion of its nonlinear characteristic, while the Y deflection current operates over the first portion of its non-linear characteristic, thereby generating the desired curved line stroke 3 illustrated in FIG. 4, without having to provide a specially shaped waveform for either of the X and Y deflection yokes.

Since, as shown in FIG. 6, a time duration of five time constants is required for the X and Y deflection currents to reach their stroke 3 endpoints, the T TIME DURATION SIGNALS 10C, for stroke 3, are chosen to provide an overall time duration of five time constants. Also, since stroke 3 is not blanked, nor is it the last stroke of the character R, the blanking signal 10D and the LAST STROKE SIGNAL 10E are not changed during stroke 3, so that a visible trace of stroke 3 appears on the face of the cathode ray tube 50, and an OUTPUT NEXT STROKE SIGNAL 62A is again produced and applied to the stroke register 10 to terminate stroke 3 and begin stroke 4.

Stroke 4 As illustrated in FIG. 4, stroke 4 of the character R is a blanked straight line (as indicated by stroke 4 being dashed), from X=4, Y=7.5 to the stroke 4 endpoint of X=0, Y=5. Stroke 4 is generated by choosing the stroke 4 data signals 10A to 10E outputed from the stroke storage register 10 as follows: the X and Y END- POINT SIGNALS 10A and 10B are chosen to provide respective steady-state X and Y values of X=0, and Y=; the T TIME DURATION SIGNALS C are chosen to provide a time duration of five time constants, as is necessary to permit the X and Y deflection currents to reach their steady-state endpoint values; the BLANKING SIG- NAL 10D is chosen to cause the intensity control circuit to blank the cathode ray tube beam during stroke 4 to prevent it from being visible; and the LAST STROKE SIGNAL 10E is chosen to be the same as for strokes 1 to 3, since stroke 4 is not the last stroke, thereby causing the OUTPUT NEXT STROKE SIGNAL '62A to again be produced and applied to the stroke register 10 to terminate stroke 4 and begin stroke 5.

It is to be noted that it is not important that stroke 4 be a straigth line, since it is blanked, but such will he the case because, as shown in FIG. 6, the X and Y deflection yoke currents operate over matched portions of their non-linear curves during stroke 4, thereby generating a straight line despite the non-linearity of the deflection yoke current characteristics.

Strokes 5 and 6 As will be evident from FIGS. 4-6, strokes 5 and 6 are generated in basically the same manner as strokes 2 and 3, respectively. Accordingly, the choice of the data signals 10A to 10E for strokes 5 and 6 will be readily apparent from the previous descriptions of strokes 2 and 3 and FIGS. 4 to 6. The only diflerence is that, during stroke 5, the steady-state Y value is retained at the 5 unit value which the Y deflection current reaches at the end of stroke 4, thereby providing the desired stroke 5 endpoint of X=3, Y=5.

Stroke 7 Stroke 7', like stroke 4, is a blanked stroke and, as will be evident from FIGS. 4 to 6, is generated in basically the same manner as is stroke 4, except that the X and Y steady-state values are chosen to now provide an endpoint of X=3, 36:5.

It will be understood that, if the character P were being generated instead of the character R, then blanked stroke 7 shown in FIG. 3 would be generated instead of blanked stroke 7 in FIG. 4, in which case, the endpoint X=3, Y=0 would be chosen for stroke 7. Since stroke 7 would then be the last stroke of the character P, the LAST STROKE SIGNAL 10E would then be chosen to cause the last stroke flip-flop to enable AND gate 64, rather than AND gate 62, thereby producing the CHARACTER COMPLETE SIGNAL 64A which is applied to the data processor 12 to indicate that generation of the character P has been completed.

Stroke 8 When the character R is to be generated, which is the example illustrated in FIGS. 5 and 6, blanked stroke 7' is caused to be generated followed by unblanked stroke 8 which, illustrated in FIG. 4, is a straight line stroke from X=3, Y=5 to X=4, Y=0. Stroke 8 is generated in basically the same manner as described for blanked strokes 4 and 7', except that the X and Y ENDPOINT SIGNALS 10A and 10B are chosen to provide an endpoint of X=4, 36:0, and BLANKING SIGNAL 10D is chosen to permit a visible trace to appear on the face of the cathode ray tube. As illustrated in FIG. 6, the X and Y deflection yoke currents operate over matched portions of their non-linear curves during stroke 8, so that stroke 8 will be a straight line, despite the non-linearity of the deflection yoke current vs. time characteristics.

Stroke 9 Stroke 9, which is the 1st stroke of the character R, is a blanked stroke from X=4, Y=0 to the stroke 9 endpoint X=0, Y=0, which is the same point as the starting point for stroke 1. Stroke 9 is generated in essentially the same manner as the other blanked strokes 4 and 7 of the character R, except that the stroke 9 endpoint is chosen as X=0, Y=0, and the LAST STROKE SIGNAL 10B is chosen to cause the last stroke flip-flop 22 to enable AND gate 64, instead of AND gate 62, thereby producing the CHARACTER COMPLETE SIGNAL 64A, instead of the OUTPUT NEXT STROKE SIGNAL 62A. The data processor 12 is, thus, advised that generation of the character R has been completed.

It will be understood that, in order for the character R to remain visible on the face of the cathode ray tube, the data processor will repeat the above described generation of the stroke of the character R at a suitable repetition rate. If it is desired that the character R be drawn at a different location on the face of the cathode ray tube 50, the data processor 12 can control the main position control circuitry 35 accordingly. If many characters are to be visible on the face of the cathode ray tube 50 at the same time, the main beam position can be appropriately controlled for this purpose in a well known manner, each character being regenerated when the main beam position arrives at its relative character starting point, the rate of character regeneration being suflicient to make the characters continuously visible.

It is also to be understood that other techniques for generating curved strokes may be used in accordance with the invention besides those exemplified for strokes 3 and 6 of the character R. For example, where desirable, any portion of a curved stroke may be used by appropriate control of the stroke time duration and/or by providing blanking for any desired portion of a stroke. It is also possible to vary the type of curvature obtained for a stroke by controlling the magnitude and time of application of the steady-state current values to obtain mismatched operation over different portions of the X and Y non-linear charcteristics. Such variations as these are to be considered as included within the scope of the present invention.

It will thus be evident that while the invention has been particularly shown and described with reference to a preferred embodiment thereof, those skilled in the art will be able to provide appropriate changes in the construction and arrangement of the invention to suit a wide variety of applications without departing from the spirit and scope of the invention.

What is claimed is:

1. In a display system,

a display means for displaying data using a variably positionable beam,

first deflection means coupled to said display means so as to cause deflection of said beam in a first direction in response to an applied signal,

second deflection means coupled to said display means so as to cause deflection of said beam in a second direction in response to an applied signal,

each of said deflection means having a non-linear deflection vs. time characteristic in response to an applied signal, controllable signal source means for applying likeshaped signals to each of said deflection means,

and control means including a data source for selecting the time of application, amplitude and time duration of the like-shaped signals applied to said deflection means by said controllable signal source means so as to permit variation of the relative portions of the non-linear characteristics of said deflection means which are operative at a given time, whereby the likeshaped signals provided by said control means can cause said display means to generate lines having diflerent curvatures.

2. The invention in accordance with claim 1, wherein the non-linear deflection vs. time characteristic of each deflection means is substantially similar,

and wherein said control means is constructed and arranged to operate in response to said data to cause said display means to generate a straight line by controlling the time of application, amplitude, and time duration of the like-shaped signals applied to said deflection means so as to provide operation over substantially the same portions of their non-linear deflection vs. time characteristics, and to cause said display means to generate a curved line by controlling the time of application, amplitude and time duration of the like-shaped signals applied to said deflection means so as to provide operation over diflerent portions of their non-linear deflection vs. time characteristics.

3. The invention in accordance with claim 2,

wherein said display means is a cathode ray tube wherein each of said deflection means is a cathode ray tube deflection means, and wherein said first and second directions are substantially at right angles. 4. The invention in accordance with claim 3, wherein each of said cathode ray tube deflection means is a magnetic deflection yoke having a deflection substantially proportional to the current flowing therein, whereby the non-linear deflection vs. time characteristic of each deflection yoke will substantially correspond to its non-linear deflection yoke current vs. time characteristic. 5. The invention in accordance with claim 4, wherein each like-shaped signal applied to a deflection yoke from said controllable signal source means has a shape which for the duration of the applied signal provides a constant amplitude steady-state current value towards which the deflection yoke current progresses in a manner governed by the non-linear deflection yoke current vs. time characteristic of the deflection yoke. 6. The invention in accordance with claim 5, whereln said data source stores data to he displayed m the form of a plurality of strokes, each stroke contaming stroke data specifying a predetermined stroke time duration and a predetermined endpoint for each deflection yoke, and wherein said control means .includes means responsive to the endpoints specified by stroke data outputed from said data source for controlling said controllable signal source means to apply a like-shaped signal to each deflection yoke which provides a steady-state current value therefor in accordance with the respective predetermined endpoint specified by the outputed stroke data, and means responsive to the stroke time duration specified by stroke data outputed from said data source for delaying outputting of the stroke data for the next stroke for a predetermined time selected in accordance with the stroke time duration specified by the outputed stroke data. 7. The invention in accordance with claim 6, wherein a predetermined plurality of strokes in said data source arranged to be outputed in a predetermined order constitute a character which is to be generated on the face of said cathode ray tube, wherein each stroke also contains data indicating whether the stroke is to be blanked and whether the stroke is the last stroke of the character, and wherein said control means also includes means for controlling the intensity of the cathode ray tube beam in response to the blanking data in an outputed stroke, and means responsive to the last stroke data contained in the stroke data of an outputed stroke for initiating outputting of the next stroke of a character by said data source after the time duration specified by the stroke data whenthe stroke is not the last stroke of the character. 8. The invention in .accordance with claim 7, wherein said data source stores and outputs stroke data in digital form, and wherein said controllable source means includes a digital-to-analog converter for each respective deflection yoke. 9. The invention in accordance with claim 7, wherein said means responsive to the stroke time duration specified by stroke data outputed from said data source includes a plurality of delay circuits providing different predetermined delays and selectable in ac cordance with the time duration specified by the outputed stroke data. 10. In a display system including a display means for displaying data in response to the movement of a variably positionable beam and having first and second deflection means cooperating therewith for deflecting said beam in respective first and second directions,

a method for causing lines of diflerent curvature to be generated by said display means using like-shaped signals applied to said deflection means, said method comprising providing each of said deflection means with a nonlinear eflection vs. time characteristic in response to an applied signal,

applying like-shaped signals at controllable times and of controllable amplitude and time duration to said deflection means,

and controlling the time of application, amplitude and duration of the like-shaped signals applied to said deflection means so as to Vary the relative portions of the non-linear characteristics of said deflection means which are operative during different time periods of line generation by said display means.

11. In a display system including a cathode ray tube and first and second magnetic deflection yokes cooperating therewith for deflecting the cathode ray tube beam in respective substantially perpendicular directions,

a method for generating a character on the face of the cathode ray tube by a plurality of successively generated strokes where a stroke may be a curved or straight line, said method comprising providing said deflection yoke with substantially similar non-linear current vs. time characteristics,

applying like-shaped signals at controllable times and of controllable amplitude and time duration to said deflection yokes,

and controlling the time of application, amplitude and time duration of the like-shaped signals applied to said deflection yokes so that for each straight line stroke the deflection yoke currents operate over substantially the same relative portions of their respective non-linear current vs. time characteristics, and for each curved line stroke the deflection yoke currents operate over different relative portions of their non-linear current vs. time characteristics.

12. The invention in accordance with claim 11,

- wherein each like-shaped signal applied to a deflection yoke has a shape which results in the deflection yoke current progressing towards a constant amplitude steady-state current value in a manner governed by the non-linear current vs. time characteristic of the deflection yoke.

References Cited UNITED STATES PATENTS 3,325,803 6/1967 Carlo-ck et al 340324.1 3,364,479 1/1968 Henderson et al. 340324.1 3,394,367 7/1968 Dye 340324.1

ALVIN H. WARING, Primary Examiner M. M. CURTIS, Assistant Examiner US. Cl. X.R. 31518, 19, 27 

